What is the diff. between pressed and loose face powder?

I have an oily t-zone, so I need powder- especially in the summer. I like translucent because I don't want the powder to add any color to my face, they are always too light or too dark. I also want a fairly natural look- I hear that pressed powder is more for shine and loose is more for a smooth finish? But loose is also SO messy, I find it so much easier to carry pressed powder and not have to deal with carrying a seperate brush and powder falling everywhere. Any advice on brands that are good? Thanks in advance!What is the diff. between pressed and loose face powder?
Sephora Brand Matifying Compact Powder, is good and inexpensive too. You can read lots of reviews on their site about it.

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